JP2007209828A - Purifying method of contaminated soil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a purifying method of contaminated soil enabling reliable and economic treatment of excavated soil contaminated with organochlorine compounds to make the soil harmless. <P>SOLUTION: The method comprises mixing, with stirring, excavated soil 1 contaminated with organochlorine compounds with a metal reducing agent containing zero-valent iron powder and water to prepare a mixture 15 and curing the mixture 15 in a container 4 for a specified period while supplying the metal reducing agent to the mixture 15 and stirring during the curing period to make the organochlorine compounds harmless. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a purification technique for soil contaminated with harmful substances, and more particularly to a purification process for soil contaminated with an organic chlorine compound such as PCB (polychlorinated biphenyl).

  Soil contaminated with organochlorine compounds represented by PCB (polychlorinated biphenyl, non-volatile hydrophobic organic compound) and the like is present in the ground such as a factory site without much decomposition.

  Further, this PCB or the like is excavated from the ground for soil purification and stored in a container such as a drum can.

  In particular, the excavated contaminated soil is stored in large quantities without being subjected to purification treatment, and the purification treatment is urgently needed.

  Conventionally known methods include, for example, a thermal decomposition method, an alkali catalytic chemical decomposition method, a melt-solidification method, and an iron powder method.

  However, it is desired to develop a method in which contaminated soil is purified so as to satisfy safety standards and the number of treatment steps is small.

  Among the various processing methods, there are the following as typical solution means.

  Electrical components such as transformers and capacitors are those that contain hardly decomposed harmful substances such as PCBs, waste liquids, and waste oils as constituent members or parts thereof.

  This harmful substance is stored in various containers such as drums and boxes, charged into a melting furnace as fuel, and melted at a high temperature to thermally decompose the harmful substance (see, for example, Patent Document 1). ).

  Further, there is a method in which after excavating soil contaminated with an organic halogen compound, iron powder is mixed into the excavated soil and piled up on the ground in a pile shape and left for several days to several months.

  There is also a method of decomposing pollutants by mixing iron powder in excavated soil and backfilling it underground to convert it into hydrocarbons containing no halogen such as ethane or ethylene.

  Furthermore, there is a treatment method for preventing recurrence of contamination due to contaminants remaining in the surrounding soil (see, for example, Patent Document 2).

  Also, dioxin-contaminated solids are pulverized with a pulverizer, the atmosphere of the pulverized product is replaced with an inert gas, and a reducing metal is introduced into the pulverized material and mixed.

Thereafter, the pulverized dioxin-contaminated mixture obtained from the pulverized product and the reducing metal is transferred to a dehalogenation treatment reactor while maintaining the inert gas atmosphere, and the pulverized product is reduced with the reducing metal. Thus, the dehalogenation reaction of dioxins is performed. (For example, refer to Patent Document 3).
JP 2004-154666 A JP 2001-577 A JP 2003-190932 A

  However, what is described in Patent Document 1 is a thermal decomposition process, which requires a high-temperature incinerator, which complicates equipment and becomes large-scale.

  Hazardous substances in this thermal decomposition treatment include devices such as PCBs, waste liquids, waste oils, etc. that are difficult to decompose (hereinafter referred to as PCBs) or contaminated with PCBs, articles such as parts, PCBs, etc. Contaminated soil, contaminated water, etc. mixed with or a container such as a drum can.

  This hazardous substance is directly burned while maintaining a high temperature in a high-temperature incinerator, and the hazardous substance is thermally decomposed. The high-temperature incinerator requires a large-scale facility that considers durability, fuel for incineration, etc. The amount of energy used increases.

  There is also a problem of undecomposed dioxins by combustion.

  Next, the thing of patent document 2 mixes iron powder with excavated soil, piles up the obtained mixture in the shape of a pile (pile), hangs a sheet, and is left still for several days to several months. is there.

  When excavating this contaminated soil, the excavated material excavated from the contaminated site contains large contaminants such as stones and glass, and components having greatly different particle sizes. For this reason, when mixing iron powder with excavated soil, it is difficult to disperse | distribute iron powder uniformly in excavated soil.

  Moreover, since the lower part of the mound of the mixture of iron powder mixed with excavated soil is in contact with the ground, the mixture may leak.

  Moreover, it is difficult for the hills formed (stacked) formed by the mixture to break down due to weathering or the like to maintain the initial shape, and the mixture is easily exposed from the sheet.

  Furthermore, the required amount of water in the mixture necessary for preventing oxidation by contact of iron powder with air and promoting reductive decomposition of the organic halogen compound cannot be maintained.

  In other words, the balance between the oxidation rate of iron powder and the reduction rate of PCB or the like changes due to the evaporation of water due to the drying of the mixture, and stable reductive decomposition of PCB or the like over a certain period is difficult.

  Furthermore, although it is a common problem of the soil purification treatment method using iron powder, hydrophobic organic chlorine compounds adhering to the soil, such as PCBs and dioxins, adhere very strongly to the soil surface.

  Even if a large amount of iron powder is mixed, as a substance, for example, the contamination concentration is halved in a relatively short period of time, but then the purification rate becomes slow and the purification process takes time.

  In particular, when the soil concentration of excavated soil is high, it becomes more difficult to completely purify the soil.

  This is considered to be due to factors such as agglomeration of iron powder over time, deterioration of the activity of the iron powder surface, and soil agglomeration.

  In addition, a large amount of iron powder is required, which is not economical and has a problem of secondary contamination.

  Moreover, the thing of patent document 3 requires the grinder which grind | pulverizes a contaminated solid substance, Furthermore, the reducing metal of metallic sodium is mixed with the grind | pulverized substance grind | pulverized with the grinder, and a dehalogenation process reaction is carried out.

  At this time, an apparatus for maintaining an inert gas or a reducing atmosphere is necessary, which complicates the entire system, resulting in a problem that the operating cost increases.

  The present invention solves the above-mentioned conventional problems, and excavated soil contaminated with PCB or the like is reliably (here, the certainty is below a reference value conforming to environmental standards), and further, iron powder It is an object of the present invention to provide a method for purifying contaminated soil, which can reduce running costs as a result and effectively meet (detoxify) environmental standards by effectively making inputs.

  The present invention provides a mixture obtained by stirring and mixing excavated soil contaminated with an organic chlorine compound, a metal reducing agent containing zero-valent iron powder, and water, and curing the mixture in a container for a certain period of time. A method for purifying contaminated soil is characterized in that a metal reducing agent is supplied to the mixture during the period and mixed with stirring to detoxify the organochlorine compound.

  According to the method for purifying contaminated soil of the present invention, a drilling soil contaminated with an organic chlorine compound typified by PCB or the like is reliably and more efficiently charged with a metal reducing agent containing zero-valent iron powder. As a result, the running cost can be reduced and processing (detoxification processing) conforming to environmental standards can be performed.

  The first invention is a mixture obtained by stirring and mixing excavated soil contaminated with an organic chlorine compound, a metal reducing agent containing zero-valent iron powder, and water, and curing this mixture in a container for a certain period of time. A method for purifying contaminated soil is characterized in that a metal reducing agent is supplied to a mixture under curing for a certain period of time in a container and mixed with stirring to detoxify an organic chlorine compound.

  As a result, it is possible to minimize degradation of the surface activity of the supplied metal reducing agent and to mix a novel metal reducing agent having no surface activity degradation during the curing period in the mixture.

  Therefore, the supplied metal reducing agent can be effectively acted on the decomposition reaction of the organic chlorine compound, and the decomposition reaction can be more averaged over the entire curing period, so that the organic chlorine compound can be reliably purified.

  Further, the mixture is stirred and mixed together with the supply of the metal reducing agent during the curing period.

  Thereby, aggregation of the metal reducing agent and soil agglomeration can be suppressed, and contact of the organic chlorine compound and the metal reducing agent can be promoted together with uniform dispersion of the metal reducing agent in the soil.

  Therefore, the supplied metal reducing agent can effectively act on the decomposition reaction of the organic chlorine compound, and the organic chlorine compound can be reliably purified.

  Furthermore, by curing in a sealed container, a stable decomposition reaction can be generated, and the contaminated soil can be reliably purified.

  Furthermore, the metal reducing agent containing the required zero-valent iron powder is minimized, and there is no need to use a larger and complicated processing apparatus.

  By suppressing the amount of the metal reducing agent containing zero-valent iron powder to a minimum (1% to 10% of the weight of the slurry-like soil), an appropriate oxidation reaction of the metal reducing agent can be performed, and excess metal The introduction of the reducing agent can be prevented, and the container storage amount in the subsequent stage becomes an appropriate amount.

  Therefore, by excavating soil contaminated with organochlorine compounds represented by PCB, etc., the iron powder oxidation reaction and slurry can be reliably treated by minimizing the amount of metal reducing agent containing zero-valent iron powder. The chlorinated mixture can be efficiently dechlorinated.

  According to a second aspect of the present invention, there is provided a method for purifying contaminated soil according to the first aspect of the present invention, wherein an elution accelerator for organochlorine compounds is supplied to the mixture and mixed with stirring during the curing period.

  Thereby, detachment | desorption and elution of the organochlorine compound adhering to the surface of excavated soil can be accelerated | stimulated, and the decomposition efficiency by a metal reducing agent can be improved more.

  This is because the slurry-like soil and the metal reducing agent containing zero-valent iron powder are stirred and mixed, and then the organochlorine compound elution promoter is mixed and then stirred and mixed again, whereby the slurry-like soil grain system is kneaded. Since the metal reducing agent containing zero-valent iron powder will be supplied after water has permeated between the soil system, hydrogen ions are likely to move due to the oxidation reaction between the iron powder and water, In addition, chlorine and hydrogen ions of an organic chlorine compound such as PCB contained in the slurry mixture easily promote the dechlorination reaction.

  Thereby, detachment | desorption and elution of the organochlorine compound adhering to the surface of excavated soil can be accelerated | stimulated, and the decomposition efficiency by a metal reducing agent can be improved more.

  According to a third aspect of the present invention, in the first or second aspect of the invention, the contaminated soil purification method is characterized in that the mixture is stirred and mixed continuously or at regular intervals during the curing period.

  As a result, the soil having a larger particle size in the slurry mixture settles at the bottom of the container, prevents the soil from agglomerating, and further prevents the metal reducing agent from agglomerating. Uniform dispersion and promotion of elution of organochlorine compounds into water can be promoted, contact between the metal reducing agent and the organochlorine compound can be promoted, and the metal reducing agent can effectively act on the decomposition of the organochlorine compound.

Hereinafter, a purification treatment method for contaminated soil according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2.
FIG. 1 is a conceptual diagram of a method for purifying contaminated soil according to the present invention, and FIG. 2 is a flowchart showing processing steps corresponding to FIG. Hereinafter, description will be given based on the drawings.

  First, the basic configuration will be described with reference to the conceptual diagram of the contaminated soil purification method of FIG. 1 and 2, excavated soil 1 contaminated with an organic chlorine compound such as PCB is transported to a sorting device 2 having a vibrating sieve 2a and a vessel 2b.

  In this sorting device 2, the mesh of the vibration sieve 2a is set to about 30 mm, for example, and a large contaminant 3 such as a relatively large stone or glass mixed in the soil remains on the vibration sieve 2a. Separated.

  The excavated soil 1 passed through the vibrating screen 2a and shaken down is accommodated in the vessel 2b.

  Note that the sorting device 2 may be a jumping screen that wave-moves the screen mat surface, or a multilayer screen that is gradually made finer.

  The sorting device 2 may use a means for fixing a sieve and moving excavated soil on the sieve or a means for applying vibration to the soil.

  The sorting device 2 is not limited to the above-described configuration, and various vibration sieve devices, rotary sieve devices (trommel) and the like that have already been put into practical use can also be used.

  Further, the mesh size of the sorting device 2 may be set to an optimum condition as appropriate according to the type and characteristics of the excavated soil 1 and the size of the contaminants. Further, depending on the state of the excavated soil 1, visual selection may be performed.

  Further, the large contaminants 3 may be removed and the particle size of the excavated soil 1 may be selected, whereby the work efficiency of the subsequent purification treatment step and the decomposition efficiency of the organic chlorine compound can be improved.

  The selection processing of the excavated soil 1 may be adopted depending on the state of the excavated soil 1, and may be omitted if the excavated soil has a relatively constant particle size without mixing of large-sized stones or galley, for example.

  It has a container 4 for storing excavated soil 1 from which large-sized contaminants 3 such as stone and glass are removed, and a lid 5 for the container 4. The lid 5 is rotationally driven by a motor 6 which is a stirring and mixing means. The agitating blade 7 is fixed, and a supply pipe 8 having an on-off valve 8a for supplying water into the container 4 is opened and connected.

  The container 4 and the lid 5 are configured to be detachable, and the lid 5 and the supply pipe 8, the lid 5, the motor 6, and the stirring blade 7 are configured to be detachable from each other.

  Further, a storage container 9 for mixing and storing a metal reducing agent containing zero-valent iron powder and water is provided. The storage container 9 has a metal reducing agent supply port 10, a water supply pipe 11, and a motor as a stirring and mixing means. 12 has a stirring blade 13 driven to rotate.

  Further, a supply pipe 14 having an on-off valve 14 a for supplying the metal reducing agent and water mixed from the storage container 9 to the container 4 is provided.

  The lid 5 and the supply pipe 14 are configured to be detachable from each other.

  With this basic configuration, the excavated soil 1 is housed in the container 4, and a metal reducing agent and water are further stirred and mixed to form a mixture 15.

  As the container 4, it is preferable to use, for example, a stainless material or a resin-coated inner surface.

  Further, the mixture 15 may be accommodated via a resin bag attached to the inner surface of the container 4. As a result, leakage of the mixture 15 due to corrosion can be prevented.

  As the container 4, for example, a drum can having a volume of about 200 liters is used.

  Further, in order to cut off the oxygen source, which is an impediment to the decomposition action of the contaminants by the metal reducing agent, it is desirable to seal the mixture 15 so as not to come into direct contact with the outside air. It is preferable to fill the upper space with the body 6.

  If the amount of water supplied to the excavated soil 1 in the container 4 is too small, it will not be able to be refined and the soil mass that has wrapped gravel will not be released, and if it is too large, the total amount will be increased and transported and stored. It is not preferable from the viewpoint. The amount of water supplied may be adjusted according to the water content of the excavated soil 1.

  Moreover, as a result of calculating | requiring the optimal mixing ratio of soil and water, although it changes with moisture content of soil, for example, with respect to soil with a moisture content of 60%, by supplying water 1.5 times by weight, slurry Soil can be obtained.

  Moreover, with respect to the soil whose water content exceeds 85%, slurry-like soil can be obtained by supplying water at a weight ratio of 1 times. Furthermore, for soil having a moisture content of 15% or less, slurry-like soil can be obtained by supplying water three times as much by weight. Moreover, what is necessary is just to use general water, such as tap water, river water, and groundwater, as water used for supply water.

  As the metal reducing agent, zero-valent fine particle iron powder is used as a base. The iron powder is made into fine particles having an average particle diameter of about 70 μm, for example, and by increasing the specific surface area, the decomposition reactivity of the organic chlorine compound can be improved.

  Further, nickel alloy, carbon-coated iron powder or the like may be used in combination, and the present invention is not limited to these including the particle diameter.

  Further, the supply amount of the metal reducing agent may be set according to the initial contamination concentration of the excavated soil 1, the decreasing tendency of the contamination concentration during the curing period, and the like.

  The amount of water mixed with the metal reducing agent in the storage container 9 is equal to or more than the saturated water amount of the particulate metal reducing agent, and is fluidized in a slurry state.

  This prevents oxidation and agglomeration due to contact of the metal reducing agent with the air, and enables uniform mixing with the slurry-like soil in the container 4 in a shorter time, so that the metal reducing agent is uniformly dispersed throughout the soil. be able to.

  Further, when the excavated soil 1 is housed in a container 4 and a metal reducing agent and water are further stirred and mixed to form a mixture 15, a surfactant or an organic solvent that is an organochlorine compound elution accelerator is contained in the container 4. May be supplied.

  The elution promoter is supplied together with water from the supply pipe 8 or 11 and is made into a mixture 15 of excavated soil 1, metal reducing agent, water, and elution promoter in the container 4.

  The elution promoter is not particularly limited as long as it is water-soluble or water-dispersible.

  The surfactant includes nonionic, anionic, cationic and amphoteric surfactants, with nonionic surfactants being particularly preferred.

  This is because it is not affected by the ionized substance dissolved in the water in the mixture 15.

  As an elution accelerator, an organic solvent such as acetone or ethanol can also be used.

  The elution promoter may be supplied directly to the mixture 15, but it is preferable to supply the elution promoter after dissolving it in water at a constant concentration in order to quickly and uniformly disperse the mixture 15.

  Next, the processing steps of the contaminated soil purification method will be described with reference to FIGS.

  First, the excavated soil 1 is removed from the large contaminants 3 such as stone and glass by the sorting device 2 (S101).

  The excavated soil 1 from which the large contaminants 3 have been removed is stored in a container 4 (S102), and a lid 5 is attached to the upper opening of the container 4. Next, after opening the on-off valve 8a for a certain period of time and supplying a certain amount of water from the supply pipe 8 into the container 4, the motor 6 is energized and the agitating blade 7 is rotationally driven to agitate and mix the excavated soil 1 and water ( S103).

  Thus, the excavated soil 1 from which the large contaminants 3 have been removed is forcibly moistened and kneaded to obtain slurry-like soil.

  Next, the metal reducing agent including zero-valent iron powder and water are stirred and mixed in the storage container 9 by the stirring blade 13 that is rotationally driven by the motor 12 that is stirring and mixing means (S104).

  Further, a predetermined amount of the metal reducing agent stirred and mixed with water is supplied from the supply pipe 14 to the slurry soil in the container 4 by opening the on-off valve 14a for a predetermined time.

  After that, the rotary drive of the stirring blade 7 is continued in the container 4 for a certain period of time, and the excavated soil 1 contaminated with the organochlorine compound, the metal reducing agent containing zero-valent iron powder, and water are stirred and mixed to form a slurry mixture. 15 (S105).

  After the slurry-like mixture 15 is formed, the mixture 15 is cured in the container 4 for a certain period (for example, several months) (S106).

  Further, during the curing period of the mixture 15 in the container 4, a metal reducing agent that is agitated and mixed with water is supplied from the supply pipe 14 into the container 4 by opening the on-off valve 14 a for a certain period of time, thereby controlling the energization of the motor 6. Then, the agitating blade 7 is rotationally driven for a certain time to agitate and mix (S107, S108, S109).

  During the curing period, the frequency of supplying and stirring and mixing the metal reducing agent to the mixture 15 in the container 4 is not particularly limited. For example, a change in the contamination concentration of the organic chlorine compound in the mixture 15 in the container 4 is detected. However, it may be performed when the concentration of contamination is above a certain value and no decrease is observed.

  Further, the metal reducing agent may be continuously supplied and stirred and mixed during the curing period.

  Further, during the curing period, the metal reducing agent is supplied to the mixture 15 in the container 4 and at the same time, a surfactant or an organic solvent which is an organochlorine compound elution accelerator is supplied to the mixture 15 and mixed with stirring.

  Further, during the curing period, the elution promoter may be supplied to the mixture 15 alone and mixed with stirring.

  By the treatment steps as described above, the detoxification treatment is performed in the container 4 by the dechlorination reaction during the curing period.

  The organochlorine compound receives (reduces) electrons on the surface of the metal reducing agent containing zero-valent iron powder, and changes to a chlorine-free compound such as acetylene to make it harmless.

  After confirming the completion of the decomposition of the organic chlorine compound, it can be backfilled or reused for concrete or the like.

  After confirming the end of the decomposition of the chlorine compound, the mixture 15 may be forcedly dehydrated or air dried.

  As described above, by supplying water to the excavated soil 1, stirring and mixing to form a slurry soil, the lump-like soil is unraveled, and the soil mass enveloping gravel and the like is released and unraveled to be refined.

  Furthermore, the organochlorine compound adhering to the surface of the soil can be separated and eluted into the supplied water by the cleaning action by the supplied water and the rubbing action of the soil soil particles.

  Further, by supplying a metal reducing agent containing zero-valent iron powder to the slurry soil and stirring and mixing to obtain a mixture 15, the finely powdered metal reducing agent is uniformly distributed between the refined soil particles having a larger specific surface area. Can be dispersed.

  Furthermore, it can be made the state which a metal reducing agent contacts easily also on the surfaces, such as gravel from which the soil lump removed.

  Moreover, the organochlorine compound eluted in water can be brought into direct contact with the metal reducing agent to promote the decomposition reaction.

  Further, even when the metal reducing agent and water are supplied to the excavated soil 1 almost simultaneously and mixed with stirring to form a slurry mixture, the above-described effects can be obtained. , By sufficiently stirring and mixing to make a slurry soil, making the soil finer, eluting the organic chlorine compound into water, supplying a metal reducing agent and continuing stirring and mixing to make mixture 15, thereby reducing metal more The agent can be dispersed uniformly throughout the soil in a short time.

  Furthermore, the amount of the metal reducing agent containing the necessary zero-valent iron powder is minimized, and it is not necessary to use a large and complicated processing apparatus.

  Therefore, the excavated soil 1 contaminated with an organic chlorine compound typified by PCB or the like can be reliably treated to an environmental standard value or less.

  Furthermore, after mixing with water and a metal reducing agent beforehand, it supplies to slurry-like soil, stirs and mixes to make the mixture 15, thereby preventing oxidation and agglomeration due to contact of the metal reducing agent with air and the metal reducing agent. It can be dispersed more uniformly in the entire soil in a short time.

  Moreover, by making it cure in the sealed container 4, the leakage of the mixture 15 can be prevented and a stable decomposition reaction can be continued.

  Further, during the curing period, the metal reducing agent stirred and mixed with water is supplied to the mixture 15 in the container 4 from the supply pipe 14 by opening the on-off valve 14a for a certain period of time, and the energization to the motor 6 is controlled. Then, the stirring blade 7 is rotationally driven for a certain time to perform stirring and mixing.

  That is, the metal reducing agent is dividedly supplied to the excavated soil 1 and stirred and mixed during the initial stage and the curing period of mixing and mixing the metal reducing agent and water into the mixture 15. .

  Conventionally, the contaminated excavated soil 1 and the total amount of the metal reducing agent supplied to the soil are mixed in an initial stage and then allowed to stand still.

  For this reason, during the curing period, it reacts with various substances present in the soil to form a film on the surface of the metal reducing agent, or it is passivated and the surface is actively degraded to inhibit the decomposition reaction of the organic chlorine compound. The total amount of the metal reducing agent mixed in the initial stage cannot effectively act on the decomposition reaction of the organic chlorine compound over the entire curing period.

  For this reason, it is difficult to reliably purify the organic chlorine compound. In addition, a larger amount of iron powder is required in the initial stage, and the curing period becomes longer.

  On the other hand, in this invention, a metal reducing agent is divided | segmented (stepwise) during a curing period including the initial stage of mixing used as the mixture 15, and it stirs and mixes. As a result, it is possible to minimize the surface activity deterioration of the supplied metal reducing agent and to allow the novel metal reducing agent having no surface activity deterioration during the curing period to be present in the mixture 15.

  Therefore, the supplied metal reducing agent can effectively act on the decomposition reaction of the organic chlorine compound, and the decomposition reaction can be more averaged over the entire curing period, so that the organic chlorine compound can be reliably purified.

  Moreover, the supply amount of the required metal reducing agent can be reduced as compared with the prior art.

  Furthermore, by supplying the metal reducing agent during the curing period, for example, when the contamination concentration is not less than a certain value and no decreasing tendency is detected while detecting the contamination concentration change of the organic chlorine compound in the mixture 15 in the container 4 The organic chlorine compound can be purified more effectively and reliably.

  In addition, a metal reducing agent having a different particle size or material may be selected and supplied at each initial stage of mixing to be the mixture 15 and at the time of supplying the metal reducing agent during the curing period. You may make it supply by changing.

  For example, in the latter half of the curing period, supply a metal reducing agent having a small particle size or a surface particle having a large surface area that is more easily penetrated between soil particles or a metal reducing agent having a higher surface reducing activity, or a metal reducing agent in the latter half of the curing period. Increase the amount of supply.

  Further, a combination of the above methods can be implemented.

  As a result, the decomposition reaction can be promoted over the entire curing period, and the organic chlorine compound can be effectively and reliably purified.

  Conventionally, the metal reducing agent is relatively uniformly dispersed in the soil at the initial stage of mixing, but it aggregates over time, and in soils with relatively fine particles such as viscous soil, Easy to granulate.

  As a result, the metal reducing agent is dispersed unevenly in the soil, and the decomposition efficiency of the organochlorine compound by the metal reducing agent is deteriorated.

  On the other hand, in this invention, the mixture 15 is stirred and mixed with the supply of the metal reducing agent during the curing period. Thereby, aggregation of the metal reducing agent and soil agglomeration can be suppressed, and the metal reducing agent can be uniformly dispersed in the soil.

  Therefore, the supplied metal reducing agent can effectively act on the decomposition reaction of the organic chlorine compound, and the organic chlorine compound can be reliably purified.

  Moreover, the supply amount of the required metal reducing agent can be further reduced.

  In addition, while the metal reducing agent is supplied during the curing period, the mixture 15 is stirred and mixed, but the mixture is stirred and mixed during the curing period including the time when the metal reducing agent is supplied. This prevents the sedimentation of the larger particle size soil in the mixture into the lower part of the container, prevents the soil from agglomerating, and prevents the metal reducing agent from agglomerating. The elution promotion of the chlorine compound into water can be promoted, the contact between the metal reducing agent and the organic chlorine compound can be promoted, and the metal reducing agent can effectively act on the decomposition of the organic chlorine compound.

  Therefore, the organic chlorine compound can be reliably treated and made harmless more economically.

  In addition, during the curing period, when supplying the metal reducing agent to the mixture 15 in the container 4, the surfactant or the organic solvent which is an elution accelerator for the organic chlorine compound is also supplied to the mixture 15 and mixed with stirring. Alternatively, during the curing period, the elution promoter is supplied alone to the mixture 15 and mixed with stirring.

  That is, the elution promoter is divided (stepwise) and supplied to the excavated soil 1 by stirring and mixing the metal reducing agent and water into the mixture 15 by mixing and mixing them during the initial stage and the curing period. To do.

  Accordingly, excessive supply of the elution promoter is suppressed, and the mixture 15 is agitated and mixed at the time of supply, thereby accelerating the detachment and elution of the organic chlorine compounds adhering to the surface of the excavated soil 1, and the metal reducing agent. The decomposition efficiency due to can be further improved.

  Further, the container 4 is separately provided and has a larger volume, for example, in a reducing agent mixing tank (not shown) or in a mixer (not shown), and excavated soil, a metal reducing agent, and water are stirred and mixed to form a mixture 15. However, as described above, the excavated soil 1, the metal reducing agent containing zero-valent iron powder, and water are stirred and mixed in the container 4 to form a slurry. The mixture 15 is further cured in the same container 4, so that the treatment process can be simplified.

  Furthermore, a stirring blade 7 that is rotationally driven by a motor 6 that is stirring and mixing means is fixed to the lid 5 of the container 4, and a supply pipe 8 having an on-off valve 8 a that supplies water into the container 4 is opened. Connected. The container 4 and the lid 5 are configured to be detachable, and the lid 5 and the supply pipe 8, and the lid 5, the motor 6 and the stirring blade 7 are configured to be detachable from each other. Can be simplified.

  As described above, according to the method for purifying contaminated soil of the present invention, the metal reducing agent is divided (stepwise) during the curing period and supplied and stirred and mixed, whereby the surface activity of the supplied metal reducing agent is increased. A novel metal reducing agent can be present in the mixture 15 that minimizes degradation and has no surface activity degradation during the curing period.

  Therefore, the total amount of the metal reducing agent to be supplied can effectively act on the decomposition reaction of the organic chlorine compound, and the decomposition reaction can be more averaged over the entire curing period, so that the organic chlorine compound can be reliably purified. .

  Furthermore, the mixture 15 is stirred and mixed with the supply of the metal reducing agent during the curing period. As a result, aggregation of the metal reducing agent and soil agglomeration can be suppressed, and contact between the organochlorine compound and the metal reducing agent can be promoted together with uniform dispersion of the metal reducing agent in the soil. Therefore, the metal reducing agent to be supplied can effectively act on the decomposition reaction of the organic chlorine compound, and the organic chlorine compound can be reliably purified.

  Furthermore, the stable decomposition reaction can be caused by curing in the sealed container 4, and the contaminated soil can be reliably purified.

  In addition, the metal reducing agent containing the necessary zero-valent iron powder is minimized, and there is no need to use a larger and complicated processing apparatus. Therefore, excavated soil contaminated with organochlorine compounds typified by PCB and the like can be reliably and economically treated and rendered harmless.

  It can be applied to a wide range of uses that require purification of soil contaminated with harmful substances.

The block block diagram of the processing method of the contaminated soil of one Example of this invention Flow chart showing processing steps corresponding to FIG.

Explanation of symbols

1 Excavated soil 2 Sorting device 2a Vibrating sieve 2b Vessel 3 Large contaminants (stone, glass)
4 Container 5 Lid 6 Motor (stirring means)
7 Stirring blade (stirring means)
8 Supply pipe 8a On-off valve 9 Storage container 10 Metal reducing agent supply port 11 Supply pipe 12 Motor (stirring means)
13 Stirring blade (stirring means)
14 Supply pipe 14a On-off valve 15 Mixture

Claims (3)

The excavated soil contaminated with organochlorine compounds, a metal reducing agent containing zero-valent iron powder, and water are stirred and mixed to form a mixture, and the mixture is cured in a container for a certain period of time, A method for purifying contaminated soil, which comprises supplying a reducing agent to a mixture and stirring and mixing to detoxify an organic chlorine compound. 2. The method for purifying contaminated soil according to claim 1, wherein an elution promoter for organochlorine compounds is supplied to the mixture and mixed with stirring during the curing period. The method for purifying contaminated soil according to claim 1 or 2, wherein the mixture is stirred and mixed continuously or at regular intervals during the curing period.

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